It's like free yoghurt day at McMaster (Haha...loving that analogy). I'd assume it's the same no matter where you go. And don't worry about missing those first year sessions, I deliberately didn't go because it was so long far out of the way for me and I turned out ok. There's really no information given in those things that you can't read in the undergraduate calendar (found here:
http://registrar.mcmaster.ca /regis...lications.html).
Here's what I'd recommend doing:
Target the courses you really want to get into that are in demand. Which courses, if any, will fill up quickly? These are your primary concerns. For instance, I know Fundamentals of Rehab, a 3rd year Kinesiology course, fills up by the time the night is done. It's limited enrollment, and a very interesting course.
Then you identify, which courses will not fill up. ie. Math courses don't tend to fill up at all (with 1 or 2 exceptions). These you could even register for during the drop and add period with no trouble at all. So going on vacation will not affect registration for these courses.
Without knowing the specific courses you're going for however, no one can answer that question...not being on the night of registration may impact you a lot, or not at all.
Depending on your program and what courses you're considering taking, you may have mostly the first type, or mostly the second...so feel free to post the courses you wanna register for and we can try to help you identify those 'hotcake' courses.
EDIT: For some reason, while reading your post I was under the impression that you were entering your second year, but upon re-reading it you seem to be entering first year?
If so, disregard my above advice...I mean it's still true, but there aren't too many 'hotcake' first year courses around. 1st year courses tend to have very large class sizes to prevent people being shut out. In my experience, as someone who didn't particularly care about awkwardly timed lectures, there isn't too big of an issue. Keep in mind that what may seem awkward to you, may be just right for someone else's schedule...And so the only concern I've ever had is courses conflicting, their lecture sessions overlapped.
The beauty part is, if you really need to get into a different time section (particularly because of conflicts), you can go make arrangements with either the professor or the undergrad advisor to bend the rules and get you in there. It's definitely doable, and you should take advantage of that.
Note that this doesn't mean they will create a new lecture time for you, it simply means if there are like 3 different lecture times and you can only get into one which conflicts with another course, then you have reason to demand special permission to enter a different lecture section. The university tends to be accomodating in this way.
(And just FYI, the reason things are so different when you get to 2nd year and above (and why it required different advice) is because courses generally only have one section, and they can fill up and leave you with a sad look on your face when you try to register for them. This doesn't really happen in first year)